To create a new Site ID, first click “Structure” within your admin toolbar.
You will be taken to the Content page. In the local actions menu, click “Blocks”.
Once on the Content Blocks page, click “Add Block”.
Then click “Site ID Banner”, this is the only type of block you will have to create and you can safely ignore the two other types.
You should now find yourself on the edit form for the new Site ID. Give your Site ID an administrative name, the path to which it links (its Home Page), and the Site ID Name (the text which it renders). Once the information has been entered, click “Save”.
Now, you simply need to add it to the Site ID region of your theme. The steps to do so have been covered in Section Managing blocks.